This disclosure relates, in general, to methods for stabilizing refractory carbides in a high temperature combustion-gas environment.
Current gas turbine performance, whether for land, sea or air uses, is limited by the allowable hot-section material temperature and the cooling penalty required to maintain the integrity of those materials. In conventional turbine systems, for instance, compressor discharge air may be used as a coolant for hot gas path components. The “hot gas path” of these turbine systems includes components such as the combustor liners and flame holding segments, stationary vanes and rotating blades of a high-pressure turbine stage, and the shrouds around the rotating blades. Composite and monolithic materials have been under development for many years to provide higher temperature capabilities of these hot gas path components, leading to higher firing temperatures and engine efficiencies. Refractory carbides, such as refractory metal carbides (MCs) and ceramic matrix composites (CMCs) are such materials. Refractory carbides have extremely high melting points. Ceramic matrix composites (CMCs) consist commonly of continuous SiC reinforcing fibers within a matrix of SiC—Si, which is made using a molten silicon infiltration process. The desirable properties of CMCs include high thermal conductivity, high matrix cracking stress, high inter-laminar strengths, and good environmental stability. Though CMCs offer higher temperature capability, up to at least 2800° F., they are still limited by environmental factors that require specialized coatings and cooling. In particular, for temperatures above 2200° F., uncoated CMCs suffer from excessive oxidation and recession. Currently, CMCs utilize an environmental bond coat (EBC) based on mullite and Ba—Sr-aluminosilicate ceramic chemistries. The EBC prevents the CMC material from loss due to recession, though with associated concerns over damage or loss of the coating.
All conventional gas turbine engines employ separate combustion systems and turbines that must be in close proximity with the combustors. The design and operability of the combustor, whether of diffusion, premixed, or combined modes, gas or liquid fuels, has great influence on the thermal management of the turbine. In addition, the thermal management of the combustor system itself can significantly contribute to the resulting gas temperature profile and pattern factors, combustion instabilities, and emissions. With the technology shift to lower emissions and zero emissions engines, new combustion strategies demand innovations in combustor and turbine structure. Additionally, there is a need for systems and methods for operations which allow for increased temperature operation while maintaining integrity and performance of the turbine components.